The magnetron of a microwave oven oscillates at a frequency of around 2.45 GHz and radiates electromagnetic interference (EMI) waves to the outside. When a radio communication device that communicates with other devices at around the frequency above, due to the EMI radiation, the communication distance is significantly shortened, or in the worst case, the radio communications are blocked. To address the problems, for example, patent literatures 1 through 3 suggest methods for avoiding the EMI radiation.
Microwave ovens generally operate on a commercial power source, such as 100V AC and 200V AC, and the alternating frequency thereof is 50 Hz or 60 Hz. A microwave oven periodically has a voltage of zero (i.e., the voltage passes the zero cross point) and the magnetron temporarily stops the oscillation at around the zero cross point. To avoid the EMI radiation, conventional radio communication devices offer data transmission synchronized with the zero cross point.
However, a conventional method has the following problems:
The effective transmission rate in avoidance communication (i.e., the data transmission synchronized with the zero cross point so as to avoid the radiation effect) decreases compared to normal communication;
The conventional devices always operate in the avoidance communication regardless of whether a microwave oven is in operation or not. Under some conditions even when the microwave oven is in operation, the normal communication allows the radio communication device to have a transmission rate higher than that in the avoidance communication. However, because conventional radio communication devices have not exactly detected the operating conditions of a microwave oven, the constant use of avoidance communication is necessary.
Some conditions mentioned above are, for example, as follows: the case where the radio communication devices communicate with each other in a short distance; the case where the magnetron has decrease in oscillation intensity by power control of a microwave oven; and the case where a microwave oven temporarily stops oscillation.
As described above, conventional methods have pending problems: an effective transmission rate is not achieved in the avoidance communication; but the constant use of avoidance communication is the reliable way to avoid the radiation interference.    PTL 1 Japanese Patent Unexamined Publication No. 2002-111603    PTL 2 Japanese Patent Unexamined Publication No. 2002-319946    PTL 1 Japanese Patent Unexamined Publication No. 2002-323222